Extrusion blown molded bottles with high stiffness and transparency

ABSTRACT

A polypropylene composition comprising a random propylene copolymer, a high melt strength polypropylene having a branching index g′ of 0.9 or less and a clarifier, wherein the polypropylene composition has a MFR 2  (230° C.) of at least 2.0 g/10 min.

This application is a National Stage of International Application No.PCT/EP2009/064037, filed Oct. 26, 2009. This application claims priorityto European Patent Application No. 08167583.7 filed on Oct. 27, 2008.The disclosures of the above applications are incorporated herein byreference.

The present inventions relates to a new polypropylene composition, itsuse and manufacture as well as to new articles comprising saidpolypropylene composition.

It is well known in the polymer field that different applicationsrequire specifically tailored polymers to achieve the individualdemanding properties. For instance a polymer used for injection moldingmust necessarily have other properties as a polymer used for blowmolding.

The extrusion blow molding process for instance is a very specialprocess that allows in a flexible and cheap way the preparation ofdifferent kind of bottles with respect to size and shape. Main drawbackin this process is that the solidification step is very special comparedto normal injection molding.

In the extrusion blow molding process a polymer melt is first extrudedthrough a tubular die into air forming a polymer tube, subsequentlyblowing up said polymer tube (typically called “parison” in thistechnical field) until the outside of the tube reaches the boundaries ofthe mold. To cover the wall of the mold fully with the blown up polymertube is rather difficult compared to injection molding because the airbetween polymer tube and mold has to be removed totally which is ademanding process step. Further the inside of the polymer tube is not incontact with the mold and therefore there is only little possibility toinfluence the inner surface structure of the tube. As a consequencethereof extrusion blown molded articles, like bottles, normally showless transparency compared to any injection molded articles. Forinstance, the surface property inside and/or outside of extrusion blownbottles is typically non-uniform (flow lines, melt fracture) leading tolower overall transparency compared to injection molded bottles orinjection stretched blown molded articles (ISBM). A certain improvementof the transparency can be achieved by visbreaking the polymer materialbut this concept has quite some limitation and can only be applied forrelatively small bottles since a certain level of melt strength isessential for proper processing. Accordingly bigger bottles (volume of11 or more) are not producible with visbroken polypropylene in anextrusion blow molding process.

Beside transparency also stiffness is very important for the performanceof a bottle. Higher stiffness would allow reducing the wall thickness ofa bottle and is also important for the filling process (no deteriorationof the bottle). Moreover a better stiffness leads also to improvedstackability. The stiffness of bottles is reflected by the so called topload (top load is the maximum force applied to a bottle before it startsto collapse).

Further it is well known that the extruded parison tends to swell interalia in wall thickness. Even though the swell effect is to some extentdesired it should not diverge too much from known reference grades, inparticular from the specific reference grade “RB307MO” of Borealis.

Thus the object of the present invention is to provide a polypropylenecomposition which enables the preparation of bottles, in particular bigsized bottles, i.e. bottles with more than 1 liter filling volume, by anextrusion blow molding process, wherein the bottles are featured by goodhaze, gloss and stiffness. Further it is desired that during thepreparation of the bottles a weight swell occurs, which differs onlylittle from known grades (i.e. “RB307MO” of Borealis) used in extrusionblow molding processes.

Accordingly the present invention is directed to polypropylenecompositions useful in extrusion blow molding processes for bottles. Inthis context it is important to note that an extrusion blow moldingprocess differs essentially from injection stretch blow moldingprocesses and thus also the employed polymers must be of differentnature, in particular in view of the melt flow behavior.

Keeping the above said in mind, the finding of the present invention isthat a visbroken polypropylene must be combined with a branchedpolypropylene, like a Y/H-shaped polypropylene, i.e. a high meltstrength polypropylene (HMS-PP) obtaining a composition with a melt flowsuitable for extrusion blow molding processes.

Accordingly the present invention is directed to a polypropylenecomposition comprising a random propylene copolymer (R-PP), a high meltstrength polypropylene (HMS-PP) and a clarifier (C), wherein

-   -   (a) the random propylene copolymer (R-PP) comprises units        derived from propylene and at least another C₂ to C₂₀ α-olefin,    -   (b) optionally the high melt strength polypropylene (HMS-PP) has        a branching index g′ of less than 1.0, preferably of 0.9 or        less,    -   (c) the clarifier (C) comprises at least one α-nucleating agent        (N), and    -   (d) the polypropylene composition has a MFR₂ (230° C.) of at        least 2.0 g/10 min, preferably a MFR₂ (230° C.) in the range of        2.0 to 6.0 g/10 min, more preferably a MFR₂ (230° C.) in the        range of 2.0 to 4.5 g/10 min.

Preferably the polypropylene composition comprises as polymer componentsonly the random propylene copolymer (R-PP) and the high melt strengthpolypropylene (HMS-PP) as defined above and in further detail below.

It has been surprisingly found out that such a polypropylene compositionhas superior properties compared to known polypropylene compositions, inparticular to those used for extrusion blown molding processes. Thepolypropylene composition of the present invention enables in particularto produce extrusion blown bottles with low haze, exceptional good glossand stiffness in terms of high top load. Further it has been observedthat the weight swell does not differ from commercial products (seetable 1).

In the following the present invention is described in more detail.

One essential requirement of the inventive polypropylene composition isits increased melt flow rate. The melt flow rate mainly depends on theaverage molecular weight. This is due to the fact that long moleculesrender the material a lower flow tendency than short molecules. Anincrease in molecular weight means a decrease in the MFR-value. The meltflow rate (MFR) is measured in g/10 min of the polymer dischargedthrough a defined die under specified temperature and pressureconditions and the measure of viscosity of the polymer which, in turn,for each type of polymer is mainly influenced by its molecular weightbut also by its degree of branching. The melt flow rate measured under aload of 2.16 kg at 230° C. (ISO 1133) is denoted as MFR₂ (230° C.).Accordingly, it is preferred that the inventive polypropylenecomposition has an MFR₂ (230° C.) of at least 2.0 g/10 min, morepreferably of at least 2.2 g/10 min. Accordingly it is in particularappreciated that the inventive polypropylene composition has a MFR₂(230° C.) in the range of 2.0 to 6.0 g/10 min, more preferably of 2.0 to4.5 g/10 min, still more preferably of 2.1 to 3.8 g/10 min, still yetmore preferably of 2.2 to 3.5 g/10 min.

Further, as stated above the new polypropylene composition must comprisea high melt strength polypropylene (HMS-PP). Such polymer types improvethe melt strength of the polypropylene composition. Accordingly it ispreferred that the polypropylene composition is further characterized bya strain hardening behavior with a haul-off force F_(max) of at least7.0 cN and a draw down velocity v_(max) of at least 180 mm/s, morepreferably by a strain hardening behavior with a haul-off force F_(max)of at least 7.5 cN and a draw down velocity v_(max) of at least 185mm/s.

Further the polypropylene composition can be additionally defined by thegel content. The gel content is a good indicator for the chemicalmodification of the polypropylene composition or its components.Accordingly the present invention is featured by relatively moderate gelcontent, i.e. of not more than 1.00 wt.-%, even more preferred of notmore than 0.80 wt.-%, still more preferred of not more than 0.50 wt.-%determined as the relative amount of polymer insoluble in boiling xylene(xylene hot insoluble fraction, XHI). On the other hand thepolypropylene composition must comprise a certain amount of high meltstrength polypropylene (HMS-PP). Accordingly the amount of gel contentin the polypropylene composition is preferably more than 0.15 wt.-%,more preferably of at least 0.27 wt.-%. Thus a preferred range for thegel content of the polypropylene composition is 0.05 to 0.90 wt.-%, like0.15 to 0.90 wt.-%, more preferred 0.26 to 0.8 wt.-%.

Further it is appreciated that the polypropylene composition is free ofany elastomeric polymer component, like an ethylene propylene rubber. Inother words the polypropylene composition shall be not a heterophasicpolypropylene composition, i.e. a system consisting of a polypropylenematrix in which an elastomeric phase is dispersed. Such systems arefeatured by a rather high xylene cold soluble content. Accordingly, thepresent polypropylene composition differs from such a heterophasicsystem by a rather low xylene cold soluble (XCS) content. Therefore thepolypropylene composition has preferably a xylene cold soluble fraction(XCS) of not more than 15.0 wt-%, more preferably of not more than 14.0wt.-%, yet more preferably of not more than 12.0 wt.-%, like not morethan 11.5 wt.-%.

Further the polypropylene composition can be specified by the amount ofcomonomer units other than propylene within the polypropylenecomposition. Accordingly it is appreciated that the amount of unitsderived from C₂ to C₂₀ α-olefins other than propylene is not more than7.0 wt.-%, preferably not more than 6.0 wt.-%, like not more than 5.5wt.-%, in the polypropylene composition.

In the following the present polypropylene composition is furtherdefined by the polymer components within the composition.

As comes already apparent from the wording used in the instant inventionthe random propylene copolymer (R-PP) is chemically different to thehigh melt strength polypropylene (HMS-PP). One essential difference isthat the random propylene copolymer (R-PP) compared to the high meltstrength polypropylene (HMS-PP) is unbranched. In other words the randompropylene copolymers (R-PP) has preferably a branching index g′ of 1.0.A further distinguishing feature between the high melt strengthpolypropylene (HMS-PP) and the random propylene copolymer (R-PP) ispreferably the gel content expressed in the amount of the xylene hotinsoluble fraction (XHI). Accordingly the random propylene copolymer(R-PP) has a gel content below 0.15 wt.-%, more preferably has nodetectable gel content.

The random propylene copolymer (R-PP) comprises units derived frompropylene and at least another C₂ to C₂₀ α-olefin, preferably at leastanother C₂ to C₁₀ α-olefin. Accordingly the random propylene copolymer(R-PP) comprises units derived from propylene and at least anotherα-olefin selected from the group consisting of ethylene C₄ α-olefin, C₅α-olefin, C₆ α-olefin, C₇ α-olefin, C₈ α-olefin, C₉ α-olefin and C₁₀α-olefin. More preferably the random propylene copolymer (R-PP)comprises units derived from propylene and at least another α-olefinselected from the group consisting of ethylene, 1-butene, 1-pentene,1-hexene, 1-heptene, 1-octene, 1-nonene and 1-decene, wherein ethylene,1-butene and 1-hexene are preferred. It is in particular preferred thatthe random propylene copolymer (R-PP) consists of units derived frompropylene and ethylene. The amount of units derived from C₂ to C₂₀α-olefins other than propylene in the random propylene copolymer (R-PP)is in the range of 1.0 to 7.0 wt.-%, more preferably 1.5 to 6.0 wt.-%,still more preferably 2.0 to 5.5 wt.-%.

Preferably the random propylene copolymer (R-PP) is isotactic.Accordingly it is appreciated that the random propylene copolymer (R-PP)has a rather high pentad concentration, i.e. higher than 90%, morepreferably higher than 92%, still more preferably higher than 93% andyet more preferably higher than 95%, like higher than 99%.

One requirement in the present invention is that units derived from C₂to C₂₀ α-olefins other than propylene within the propylene copolymer(R-PP) are randomly distributed. The Randomness indicates the amount ofisolated comonomer units, i.e. those which have no other comonomer unitsin the neighbour, compared to the total amount of comonomers in thepolymer chain. In a preferred embodiment, the randomness of the randompropylene copolymer (R-PP) is at least 30%, more preferably at least50%, even more preferably at least 60%, and still more preferably atleast 65%.

Further it is appreciated that the xylene soluble content of the randompropylene copolymer (R-PP) is a rather low. Accordingly the randompropylene copolymer (R-PP) has preferably a xylene cold soluble fraction(XCS) measured according to ISO 6427 (23° C.) of not more than 14.0wt-%, more preferably of not more than 13.0 wt.-%, yet more preferablyof not more than 12.0 wt.-%, like not more than 11.5 wt.-%. Thus apreferred range is 1.0 to 14.0 wt.-%, more preferred 1.0 to 13.0 wt.-%,still more preferred 1.2 to 11.0 wt.-%.

The random propylene copolymer (R-PP) can be unimodal or multimodal,like bimodal in view of the molecular weight distribution and/or thecomonomer content distribution.

When the matrix is unimodal with respect to the molecular weightdistribution and/or comonomer content, it may be prepared in a singlestage process e.g. as slurry or gas phase process in a slurry or gasphase reactor. Preferably, the unimodal the random propylene copolymer(R-PP) is polymerized as a slurry polymerization. Alternatively, theunimodal the random propylene copolymer (R-PP) may be produced in amultistage process using at each stage process conditions which resultin similar polymer properties.

The expression “multimodal” or “bimodal” used herein refers to themodality of the polymer, i.e.

-   -   the form of its molecular weight distribution curve, which is        the graph of the molecular weight fraction as a function of its        molecular weight,        or more preferably    -   the form of its comonomer content distribution curve, which is        the graph of the comonomer content as a function of the        molecular weight of the polymer fractions.

As will be explained below, the polymer components of the randompropylene copolymer (R-PP) can be produced in a sequential step process,using reactors in serial configuration and operating at differentreaction conditions. As a consequence, each fraction prepared in aspecific reactor will have its own molecular weight distribution and/orcomonomer content distribution.

When the distribution curves (molecular weight or comonomer content)from these fractions are superimposed to obtain the molecular weightdistribution curve or the comonomer content distribution curve of thefinal polymer, these curves may show two or more maxima or at least bedistinctly broadened when compared with curves for the individualfractions. Such a polymer, produced in two or more serial steps, iscalled bimodal or multimodal, depending on the number of steps.

Accordingly the random propylene copolymer (R-PP) may be multimodal,like bimodal, in view of the comonomer content and/or molecular weight.It is in particular appreciated that the random propylene copolymer(R-PP) is multimodal, like bimodal, in view of the comonomer content.

Further in case the random propylene copolymer (R-PP) is of multimodal,like bimodal, character, in particular multimodal, like bimodal, in viewof the comonomer content, it is appreciated that the individualfractions are present in amounts influencing the properties of thematerial. Accordingly it is appreciated that each of these fractions isat least present in the amount of 10 wt.-% based on the random propylenecopolymer (R-PP). Accordingly in case of a bimodal system, in particularin view of the comonomer content, the split of the two fractions isroughly 50:50.

Thus in one embodiment the random propylene copolymer (R-PP) comprisestwo fractions which differ in their comonomer content, like ethylenecontent (preferably as the only comonomer in the random propylenecopolymer (R-PP)), wherein the first fraction is present from 40 to 60wt.-% and the second fraction from 60 to 40 wt.-%. In such a case therandom propylene copolymer (R-PP) comprises at least two fractions, morepreferably consists of two fractions, that have a comonomer content,like ethylene content, which differ of at least 2.0 wt.-%, morepreferably differ of at least 2.5 wt.-%. On the other hand thedifference in the comonomer content in the two fractions should be nottoo high, i.e. not higher than 6.0 wt.-%, preferably not higher than 5.0wt %, to avoid any separation tendencies. Thus it is appreciated thatthe random propylene copolymer (R-PP) comprises at least two fractions,more preferably consists of two fractions, that have comonomer contentswhich differ of 2.0 to 6.0 wt.-%, more preferably of 2.5 to 5.0 wt.-%.Accordingly in one embodiment the random propylene copolymer (R-PP)consists of a first fraction being a propylene homopolymer and a secondfraction being a propylene copolymer having a comonomer content,preferably ethylene content, of at least 2.0 wt.-%, more preferably ofat least 3.0 wt.-%, like at least 3.5 wt.-%.

In particular suitable random propylene copolymers (R-PP) are those asfor instance described in EP 1 580 207 A1 and WO 2003/002639 A1.

As stated above, the inventive polypropylene composition must at leastcomprise—as polymer components—a random propylene copolymer (R-PP) and ahigh melt strength polypropylene (HMS-PP). The two components must bechosen in such a way that in particular the required MFR₂ (230° C.) ofat least 2.0 g/10 min for the final polypropylene composition is met. Inprinciple three options are possible to achieve the desired rather highmelt flow rate for the final composition. First one uses a randompropylene copolymer (R-PP) with a MFR₂ (230° C.) similar to the finalproduct and mix it with the high melt strength polypropylene (HMS-PP).An alternative route is to take a random propylene copolymer (R-PP)having a significantly lower MFR₂ (230° C.) compared to the finalproduct, degrading said random propylene copolymer (R-PP), i.e.visbreaking, said random propylene copolymer (R-PP), and subsequentlymixing it with the high melt strength polypropylene (HMS-PP). A furtheroption is to use a mixture of a random propylene copolymer (R-PP) andthe high melt strength polypropylene (HMS-PP) (optionally with theclarifier (C)), wherein said random propylene copolymer (R-PP) has asignificantly lower MFR₂ (230° C.) compared to the final product. Saidmixture is visbroken by using peroxide to the required MFR₂ (230° C.) ofat least 2.0 g/10 min for the final polypropylene composition. Thelatter option is the most preferred.

Accordingly, considering the different options to create a polypropylenecomposition with a MFR₂ (230° C.) of at least 2.0 g/10 min, the randompropylene copolymer (R-PP) within the polypropylene composition haspreferably a MFR₂ (230° C.) of not more than 6.0 g/10 min, like 4.5 g/10min. More preferably the random propylene copolymer (R-PP) within thepolypropylene composition has a MFR₂ (230° C.) of not more than 3.0 g/10min. Accordingly it is in particular appreciated that the randompropylene copolymer (R-PP) within the polypropylene composition has aMFR₂ (230° C.) in the range of 2.0 to 6.0 g/10 min, more preferably of2.0 to 4.5 g/10 min, yet more preferably of 2.1 to 3.8 g/10 min, stillmore preferably of 2.2 to 3.5 g/10 min.

In case the inventive polypropylene composition is obtained byvisbreaking the random propylene copolymer (R-PP) or by visbreaking thepolypropylene composition, the used random propylene copolymer (R-PP)has a MFR₂ (230° C.) of at least 0.5 g/10 min, more preferably in therange of 0.5 to 3.0 g/10 min, yet more preferably of 1.0 to 2.5 g/10min, like 1.3 to 2.0 g/10 min. Preferably the initially used randompropylene copolymer (R-PP) is chosen in such a manner that thevisbreaking ratio (final MFR₂ (230° C.)/initial MFR₂ (230° C.)) is 1.3to 3.0, more preferably 1.4 to 2.5, wherein

“initial MFR₂ (230° C.)” is the MFR₂ (230° C.) of the random propylenecopolymer (R-PP) before visbreaking and

“final MFR₂ (230° C.)” is the MFR₂ (230° C.) of the random propylenecopolymer (R-PP) after visbreaking and/or the MFR₂ (230° C.) of thepolypropylene composition after visbreaking.

The preparation of the random propylene copolymer (R-PP) as well as thevisbreaking will be defined in more detail below.

As a further essential requirement of the present invention a high meltstrength polypropylene (HMS-PP) must be used. Such polymer types arecharacterized by a certain degree of branching. Possible high meltstrength polypropylenes (HMS-PP) are so called Y/H-polypropylenes andfor instance described in EP 0 787 750, i.e. single branchedpolypropylene types (Y polypropylenes having a backbone with a singlelong side-chain and an architecture resembles a “Y”) and polypropylenetypes in which polymer chains are coupled with a bridging group (anarchitecture resembles a “H”). Such polypropylenes are characterized byrather high melt strength. A parameter of the degree of branching is thebranching index g′. The branching index g′ correlates with the amount ofbranches of a polymer. The branching index g′ is defined asg′=[IV]_(br)/[IV]_(lin) in which g′ is the branching index, [IV]_(br) isthe intrinsic viscosity of the branched polypropylene and [IV]_(lin) isthe intrinsic viscosity of the linear polypropylene having the sameweight average molecular weight (within a range of ±10%) as the branchedpolypropylene. Thereby, a low g′-value is an indicator for a highbranched polymer. In other words, if the g′-value decreases, thebranching of the polypropylene increases. Reference is made in thiscontext to B. H. Zimm and W. H. Stockmeyer, J. Chem. Phys. 17, 1301(1949). This document is herewith included by reference. Thus it ispreferred that the branching index g′ of the high melt strengthpolypropylene (HMS-PP) shall be less than 1.0, more preferably equal orless than 0.9, like less than 0.8. In another preferred embodiment thebranching index g′ of the high melt strength polypropylene (HMS-PP)shall be preferably less than 0.7.

The high degree of branching of the high melt strength polypropylene(HMS-PP) contributes also to its melt strength. Accordingly it ispreferred that the high melt strength polypropylene (HMS-PP) is furthercharacterized by a strain hardening behavior with a haul-off forceF_(max) of at least 10.0 cN and a draw down velocity v_(max) of at least200 mm/s, more preferably by a strain hardening behavior with a haul-offforce F_(max) of at least 20.0 cN and a draw down velocity v_(max) of atleast 250 mm/s, yet more preferably by a strain hardening behavior witha haul-off force F_(max) of at least 25.0 cN and a draw down velocityv_(max) of at least 250 mm/s.

Such a high melt strength polypropylene (HMS-PP) is preferably obtainedby modifying, i.e. chemically modifying, a polypropylene. Such amodification is necessary to achieve the branching structure and/or thestrain hardening phenomena of the high melt strength polypropylene(HMS-PP). Such a modification has also influence on the gel content ofthe high melt strength polypropylene (HMS-PP). Accordingly it isjustified to define the high melt strength polypropylene (HMS-PP)further and/or alternatively by its gel content. Thus it is appreciatedthat the high melt strength polypropylene (HMS-PP) is featured by arelatively moderate gel content, i.e. of not more than 1.00 wt.-%, evenmore preferred of not more than 0.80 wt.-%, still more preferred of notmore than 0.50 wt.-% determined as the relative amount of polymerinsoluble in boiling xylene (xylene hot insoluble fraction, XHI). On theother hand the high melt strength polypropylene (HMS-PP) may show acertain degree of branching and thus a certain amount of gel content,i.e. of at least 0.15 wt.-%, more preferably of at least 0.27 wt.-%.Thus a preferred range for the gel content of the high melt strengthpolypropylene (HMS-PP) is 0.05 to 0.90 wt.-%, more preferred 0.26 to 0.8wt.-%. Additionally it is preferred that in the melt strengthpolypropylene (HMS-PP) has an MFR₂ (230° C.) in a range of 1.0 to 10.0g/10 min, more preferably of 4.0 to 8.5 g/10 min, still more preferablyof 6.0 to 8.0 g/10 min.

Preferably, the high melt strength polypropylene (HMS-PP) has a densityof at least 850 kg/m³, more preferably of at least 875 kg/m³ and mostpreferably of at least 900 kg/m³.

Further, preferably, the high melt strength polypropylene (HMS-PP) has adensity of not more than 950 kg/m³, more preferably of not more than 925kg/m³ and most preferably of not more than 910 kg/m³.

Preferably, the high melt strength polypropylene (HMS-PP) has a meltingpoint of at least 140° C., more preferably of at least 150° C. and mostpreferably of at least 160° C.

As stated above, the melt strength polypropylene (HMS-PP) is preferablya modified polypropylene. Accordingly the melt strength polypropylene(HMS-PP) can be further defined by the way obtained. Thus the meltstrength polypropylene (HMS-PP) is preferably the result of treating anunmodified polypropylene (A) with thermally decomposing radical-formingagents and/or with ionizing radiation. However in such a case a highrisk exists that the polypropylene (A) is degraded, which isdetrimental. Thus it is preferred that the modification is accomplishedby the use of bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s) aschemically bound bridging unit(s). A suitable method to obtain the meltstrength polypropylene (HMS-PP) is for instance disclosed in EP 0 787750, EP 0 879 830 A1 and EP 0 890 612 A2. All documents are herewithincluded by reference. Thereby, the amount of peroxide is preferably inthe range of 0.05 to 3.00 wt.-% based on the unmodified polypropylene(A).

Accordingly in one preferred embodiment the high melt strengthpolypropylene (HMS-PP) comprises units derived from

-   (i) propylene and-   (ii) bifunctionally unsaturated monomer(s) and/or multifunctionally    unsaturated low molecular weight polymer(s).

“Bifunctionally unsaturated or multifunctionally unsaturated” as usedabove means preferably the presence of two or more non-aromatic doublebonds, as in e.g. divinylbenzene or cyclopentadiene or polybutadiene.Only such bi- or multifunctionally unsaturated compounds are used whichcan be polymerized preferably with the aid of free radicals. Theunsaturated sites in the bi- or multifunctionally unsaturated compoundsare in their chemically bound state not actually “unsaturated”, becausethe double bonds are each used for a covalent bond to the polymer chainsof the polypropylene (A).

Reaction of the bifunctionally unsaturated monomer(s) and/ormultifunctionally unsaturated low molecular weight polymer(s),preferably having a number average molecular weight (M_(n))≦10000 g/mol,synthesized from one and/or more unsaturated monomers with the propylenepolymer composition may be performed in the presence of a thermally freeradical forming agent, e.g. decomposing free radical-forming agent, likea thermally decomposable peroxide and/or ionizing radiation or microwaveradiation.

The bifunctionally unsaturated monomers may be

-   -   divinyl compounds, such as divinylaniline, m-divinylbenzene,        p-divinylbenzene, divinylpentane and divinylpropane;    -   allyl compounds, such as allyl acrylate, allyl methacrylate,        allyl methyl maleate and allyl vinyl ether;    -   dienes, such as 1,3-butadiene, chloroprene, cyclohexadiene,        cyclopentadiene, 2,3-dimethylbutadiene, heptadiene, hexadiene,        isoprene and 1,4-pentadiene;    -   aromatic and/or aliphatic bis(maleimide) bis(citraconimide) and        mixtures of these unsaturated monomers.

Especially preferred bifunctionally unsaturated monomers are1,3-butadiene, isoprene, dimethyl butadiene and divinylbenzene.

The multifunctionally unsaturated low molecular weight polymer,preferably having a number average molecular weight (M_(n))≦10000 g/molmay be synthesized from one or more unsaturated monomers.

Examples of such low molecular weight polymers are

-   -   polybutadienes, especially where the different microstructures        in the polymer chain, i.e. 1,4-cis, 1,4-trans and 1,2-(vinyl)        are predominantly in the 1,2-(vinyl) configuration    -   copolymers of butadiene and styrene having 1,2-(vinyl) in the        polymer chain.

A preferred low molecular weight polymer is polybutadiene, in particulara polybutadiene having more than 50.0 wt.-% of the butadiene in the1,2-(vinyl) configuration.

The high melt strength polypropylene (HMS-PP) may contain more than onebifunctionally unsaturated monomer and/or multifunctionally unsaturatedlow molecular weight polymer. Even more preferred the amount ofbifunctionally unsaturated monomer(s) and multifunctionally unsaturatedlow molecular weight polymer(s) together in the high melt strengthpolypropylene (HMS-PP) is 0.01 to 10.0 wt.-% based on said high meltstrength polypropylene (HMS-PP).

As stated above it is preferred that the bifunctionally unsaturatedmonomer(s) and/or multifunctionally unsaturated low molecular weightpolymer(s) are used in the presence of a thermally decomposing freeradical-forming agent.

Peroxides are preferred thermally decomposing free radical-formingagents. More preferably the thermally decomposing free radical-formingagents are selected from the group consisting of acyl peroxide, alkylperoxide, hydroperoxide, perester and peroxycarbonate.

The following listed peroxides are in particular preferred:

Acyl peroxides: benzoyl peroxide, 4-chlorobenzoyl peroxide,3-methoxybenzoyl peroxide and/or methyl benzoyl peroxide.

Alkyl peroxides: allyl t-butyl peroxide, 2,2-bis(t-butylperoxybutane),1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,n-butyl-4,4-bis(t-butylperoxy) valerate, diisopropylaminomethyl-t-amylperoxide, dimethylaminomethyl-t-amyl peroxide,diethylaminomethyl-t-butyl peroxide, dimethylaminomethyl-t-butylperoxide, 1,1-di-(t-amylperoxy)cyclohexane, t-amyl peroxide,t-butylcumyl peroxide, t-butyl peroxide and/or 1-hydroxybutyl n-butylperoxide.

Peresters and peroxy carbonates: butyl peracetate, cumyl peracetate,cumyl perpropionate, cyclohexyl peracetate, di-t-butyl peradipate,di-t-butyl perazelate, di-t-butyl perglutarate, di-t-butyl perthalate,di-t-butyl persebacate, 4-nitrocumyl perpropionate, 1-phenylethylperbenzoate, phenylethyl nitro-perbenzoate,t-butylbicyclo-(2,2,1)heptane percarboxylate, t-butyl-4-carbomethoxyperbutyrate, t-butylcyclobutane percarboxylate, t-butylcyclohexylperoxycarboxylate, t-butylcyclopentyl percarboxylate,t-butylcyclopropane percarboxylate, t-butyldimethyl percinnamate,t-butyl-2-(2,2-diphenylvinyl) perbenzoate, t-butyl-4-methoxyperbenzoate, t-butylperbenzoate, t-butylcarboxycyclohexane, t-butylpernaphthoate, t-butyl peroxyisopropylcarbonate, t-butyl pertoluate,t-butyl-1-phenylcyclopropyl percarboxylate,t-butyl-2-propylperpentene-2-oate, t-butyl-1-methylcyclopropylpercarboxylate, t-butyl-4-nitrophenyl peracetate, t-butylnitrophenylperoxycarbamate, t-butyl-N-succiimido percarboxylate, t-butylpercrotonate, t-butyl permaleic acid, t-butyl permethacrylate, t-butylperoctoate, t-butyl peroxyisopropylcarbonate, t-butyl perisobutyrate,t-butyl peracrylate and/or t-butyl perpropionate.

Or mixtures of these above listed free radical-forming agents.

The unmodified polypropylene (A) to prepare such a high melt strengthpolypropylene (HMS-PP) has preferably a MFR₂ (230° C.) in a range of0.05 to 45.00 g/10 min. More preferably the MFR₂ (230° C.) is in a rangeof 0.05 to 35.00 g/10 min in case the unmodified polypropylene (A) is ahomopolymer. On the other hand the MFR₂ (230° C.) is in a range of 0.05to 45.00 g/10 min in case the unmodified polypropylene (A) is acopolymer.

Preferably the unmodified polypropylene (A) is a homopolymer. Theexpression homopolymer used in the instant invention relates to apolypropylene that consists substantially, i.e. of at least 97 wt.-%,preferably of at least 98 wt.-%, more preferably of at least 99 wt.-%,still more preferably of at least 99.8 wt.-% of propylene units. In apreferred embodiment only propylene units in the propylene homopolymerare detectable. The comonomer content can be determined with FT infraredspectroscopy, as described below in the examples.

Preferably the high melt strength polypropylene (HMS-PP) is producedfrom the unmodified polypropylene (A) as defined above under processconditions as defined in detail below.

Another essential requirement of the present invention is thatpolypropylene composition comprises a clarifier (C) comprising at leastone α-nucleating agent (N). More preferably the clarifier (C) consistsof at least one α-nucleating agent (N). Accordingly the clarifier (C)may comprise, preferably consists of, one, two or three α-nucleatingagent(s) (N). However it is appreciated that the clarifier (C) isα-nucleating agent (N).

In principle any α-nucleating agent (N) can be used.

Examples of suitable α-nucleating agents are selected from the groupconsisting of

-   (i) salts of monocarboxylic acids and polycarboxylic acids, e.g.    sodium benzoate or aluminum tert-butylbenzoate, and-   (ii) dibenzylidenesorbitol (e.g. 1,3:2,4 dibenzylidenesorbitol) and    C₁-C₈-alkyl-substituted dibenzylidenesorbitol derivatives, such as    methyldibenzylidenesorbitol, ethyldibenzylidenesorbitol or    dimethyldibenzylidenesorbitol (e.g. 1,3:2,4 di(methylbenzylidene)    sorbitol),    nonitol,1,2,3,-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol,    and-   (iii) salts of diesters of phosphoric acid, e.g. sodium    2,2′-methylenebis(4,6,-di-tert-butylphenyl) phosphate or    aluminium-hydroxy-bis[2,2′-methylene-bis(4,6-di-t-butylphenyl)phosphate],    and-   (iv) vinylcycloalkane polymer and vinylalkane polymer.

Such additives are generally commercially available and are described,for example, in Gachter/Muller, Plastics Additives Handbook, 4thEdition, Hansa Publishers, Munich, 1993.

The nucleating agent content of the polypropylene composition ispreferably up to 5 wt.-%. In a preferred embodiment, the polypropylenecomposition of the present invention contain from 0.01 to 1.0 wt.-%,preferably from 0.02 to 0.50 wt.-%, of a α-nucleating, in particulardibenzylidenesorbitol (e.g. 1,3:2,4 dibenzylidene sorbitol) or adibenzylidenesorbitol derivative, preferablydimethyldibenzylidenesorbitol (e.g. 1,3:2,4 di(methylbenzylidene)sorbitol) and/ornonito-1,1,2,3,-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol,

The most preferred α-nucleating isnonito-1,1,2,3,-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol.Accordingly in a especially preferred embodiment the clarifier (C)comprises, even more preferred consists of,nonito-1,1,2,3,-trideoxy-4,6:5,7-bis-0-[(4-propylphenyl)methylene]-nonitol.

In case the α-nucleating agents are polymeric α-nucleating agentsselected from the group consisting of vinylcycloalkane polymers andvinylalkane polymers, these polymeric nucleating agents are eitheraccomplished by a special reactor technique, where the catalyst isprepolymerised with monomers like e.g. vinylcyclohexane (VCH), or byblending the polypropylene composition with the vinylcycloalkane polymeror vinylalkane polymer. These methods are described in greater detail ine.g. EP 0 316 187 A2 and WO 99/24479

To obtain especially good results the required components as definedabove may be present in specific amounts within the new polypropylenecomposition. Thus it is preferred that the polypropylene compositionaccording to the instant invention comprises

-   -   (a) 70.0 to 95.0 wt.-%, preferably 75.0 to 93.0 wt.-%, of the        random propylene copolymer (R-PP), and    -   (b) 5.0 to 20.0 wt.-%, more preferably 6.0 to 15.0 wt.-%, of the        high melt strength polypropylene (HMS-PP), and    -   (c) 0.01 to 5.0 wt.-%, more preferably 0.02 to 1.0 wt.-%, of the        clarifier (C), based on the total polypropylene composition.

The polypropylene composition of the present invention may comprisefurther components. However it is preferred that the polypropylenecomposition comprises as polymer components only the random propylenecopolymer (R-PP) and the high melt strength polypropylene (HMS-PP) asdefined above. Accordingly the amounts of the random propylene copolymer(R-PP), the high melt strength polypropylene (HMS-PP) and the clarifier(C) may not result in 100 wt.-% based on the total polypropylenecomposition. Thus the remaining part up 100.0 wt.-% may be accomplishedby further additives known in the art. However this remaining part shallbe not more than 10.0 wt.-% within the total composition. For instancethe inventive polypropylene composition may comprise additionally smallamounts of stabilizers, acid scavengers, lubricants and mold releaseagents, fillers, nucleating agents, antistatics, plasticizers, dyes,pigments or flame retardants. In general, these are incorporated duringgranulation of the pulverulent product obtained in the polymerization.

The present invention is also directed to the use of the above definedpolypropylene composition. Accordingly the polypropylene composition asdefined in the instant invention is used for the preparation ofextrusion blown molded products. Thus the present invention is notdirected to other blow molding processes, like the injection stretchblow molding process. More particularly the present invention isdirected to the use of the polypropylene composition of the instantinvention to improve the haze and/or gloss of extrusion blown moldedarticles, like extrusion blown molded bottles, i.e. extrusion blownmolded bottles with a filling volume of 1 liter or more, made out ofsaid polypropylene composition compared to conventional extrusion blownmolded bottles, in particular compared to extrusion blown molded bottlesmade out of the commercial product “RB307MO” of Borealis. Moreover theuse of the polypropylene composition of the instant invention shallpreferably and additionally improve the top load of extrusion blownmolded articles, like extrusion blown molded bottles, i.e. extrusionblown molded bottles with a filling volume of 1 liter or more, made outof said polypropylene composition compared to conventional extrusionblown molded bottles. Accordingly the present invention is in particulardirected to the use of polypropylene composition of the instantinvention to accomplish at least one requirement, preferably allrequirements, selected from the group consisting of a haze of below 14%,more preferably below 11%, a gloss (inside and/or outside of the bottle)of at least 16%, more preferably at least 19%, and top load of at least280 N, more preferably at least 300 N, for extrusion blown moldedarticles, like extrusion blown molded bottles, i.e. extrusion blownmolded bottles with a filling volume of 1 liter or more.

Further the present invention is directed to extrusion blown moldedarticles comprising, preferably comprising at least 90 wt.-%, morepreferably consisting of, a polypropylene composition according to thisinvention. More particularly the present invention is directed tobottles, especially to bottles with a filling volume of 1 liter or more,produced by an extrusion blown process comprising, preferably comprisingat least 90 wt.-%, more preferably consisting of, a polypropylenecomposition according to this invention.

In the following the preparation of the inventive polypropylenecomposition is described in more detail.

The individual components used for the inventive polypropylenecomposition are known by the person skilled in the art and thus can bereadily produced by the information provided herein.

For instance the random propylene copolymer (R-PP) as defined in theinstant invention may be prepared by polymerizing, in a slurry reactor,for example a loop reactor, propylene optionally together with at leastanother C₂ to C₂₀ α-olefin (comonomers), in the presence of apolymerization catalyst to produce a part of the random propylenecopolymer (R-PP). This part is then transferred to a subsequent gasphase reactor, wherein in the gas phase reactor propylene is reacted inthe presence of suitably selected other C₂ to C₂₀ α-olefin(s)(comonomers) in order to produce a further part in the presence of thereaction product of the first step. This reaction sequence provides areactor blend of parts (i) and (ii) constituting a random propylenecopolymer (R-PP). It is of course possible by the present invention thatthe first reaction is carried out in a gas phase reactor while thesecond polymerization reaction is carried out in a slurry reactor, forexample a loop reactor. It is furthermore also possible to reverse theorder of producing parts (i) and (ii), which has been described above inthe order of first producing part (i) and then producing part (ii). Theabove-discussed process, comprising at least two polymerization steps,is advantageous in view of the fact that it provides easily controllablereaction steps enabling the preparation of a desired reactor blend. Thepolymerization steps may be adjusted, for example by appropriatelyselecting monomer feed, comonomer feed, hydrogen feed, temperature andpressure in order to suitably adjust the properties of thepolymerization products obtained. It is in particular possible to obtaina multimodality, preferably the bimodality, of the random propylenecopolymer (R-PP), with respect to the comonomer, like ethylene,distribution as well as with respect to the molecular weights and MFR₂(230° C.) values during said multistage polymerization procedures.

Such a process can be carried out using any suitable catalyst for thepreparation of the random propylene copolymer (R-PP). Preferably, theprocess as discussed above is carried out using a Ziegler-Nattacatalyst, in particular a high yield Ziegler-Natta catalyst (so-calledfourth and fifth generation type to differentiate from low yield, socalled second generation Ziegler-Natta catalysts). A suitableZiegler-Natta catalyst to be employed in accordance with the presentinvention comprises a catalyst component, a co-catalyst component and atleast one electron donor (internal and/or external electron donor,preferably at least one external donor). Preferably, the catalystcomponent is a Ti—Mg-based catalyst component and typically theco-catalyst is an Al-alkyl based compound. Suitable catalysts are inparticular disclosed in U.S. Pat. No. 5,234,879, WO 92/19653, WO92/19658 and WO 99/33843.

Preferred external donors are the known silane-based donors, such asdicyclopentyl dimethoxy silane or cyclohexyl methyldimethoxy silane.

One embodiment of a process as discussed above is a loop-gas phaseprocess, such as developed by Borealis, known as Borstar® technology,described for example in EP 0 887 379 A1 and WO 92/12182.

With respect to the above-mentioned preferred slurry-gas phase process,the following general information can be provided with respect to theprocess conditions.

Temperature of from 40 to 110° C., preferably between 60 and 100° C., inparticular between 80 and 90° C., with a pressure in the range of from20 to 80 bar, preferably 30 to 60 bar, with the option of addinghydrogen in order to control the molecular weight. The reaction productof the slurry polymerization, which preferably is carried out in a loopreactor, is then transferred to the subsequent gas phase reactor,wherein the temperature preferably is within the range of from 50 to130° C., more preferably 80 to 100° C., at a pressure in the range offrom 5 to 50 bar, preferably 15 to 35 bar, again with the option ofadding hydrogen in order to control the molecular weight.

The residence time can vary in the reactor zones identified above. Inembodiments, the residence time in the slurry reaction, for example theloop reactor, is in the range of from 0.5 to 5 hours, for example 0.5 to2 hours, while the residence time in the gas phase reactor generallywill be from 1 to 8 hours.

The properties of the random propylene copolymer (R-PP) produced withthe above-outlined process may be adjusted and controlled with theprocess conditions as known to the skilled person, for example by one ormore of the following process parameters: temperature, hydrogen feed,comonomer feed, propylene feed, catalyst, type and amount of externaldonor, split between two or more components of a multimodal polymer.

The high melt strength polypropylene (HMS-PP) is preferably obtained bya process as described in EP 0 879 830 A1 and EP 0 890 612 A2. Bothdocuments are herewith included by reference. Accordingly the high meltstrength polypropylene (HMS-PP) is produced by

-   (a) mixing    -   (i) a unmodified propylene homopolymer and/or copolymer (A) as        defined above, preferably a unmodified propylene homopolymer        with a weight average molecular weight (M,) of 500,000 to        1,500,000 g/mol,    -   (ii) from 0.05 to 3 wt.-% based on the components of (i) and        (ii), of a peroxide selected from the group consisting of acyl        peroxide, alkyl peroxide, hydroperoxide, perester and        peroxycarbonate, and    -   (iii) optionally diluted with inert solvents,-   (b) heating to 30 to 100° C., preferably to 60 to 90° C.,-   (c) sorption of volatile bifunctional monomers, preferably    ethylenically unsaturated, multifunctional monomers, like C₄ to C₁₀    dienes and/or C₇ to C₁₀ divinyl compounds, by the unmodified    propylene homopolymer and/or copolymer (A), preferably unmodified    propylene homopolymer (A), from the gas phase at a temperature of    from 20 to 120° C., preferably of from 60 to 100° C., where the    amount of the absorbed bifunctionally unsaturated monomers is from    0.01 to 10.00 wt.-%, preferably from 0.05 to 2.00 wt.-%, based on    the propylene homopolymer (A),-   (d) heating and melting the polypropylene composition in an    atmosphere comprising inert gas and/or the volatile bifunctional    monomers, from sorption temperature to 210° C., whereupon the    free-radical generators are decomposed and then-   (e) heating the melt up to 280° C. in order to remove unreacted    monomers and decomposition products, and-   (f) agglomerating the melt.

The process for producing the high melt strength polypropylene (HMS-PP)preferably is a continuous method, performed in continuous reactors,mixers, kneaders and extruders. Batchwise production of the high meltstrength polypropylene (HMS-PP), however is feasible as well.

Practical sorption times τ of the volatile bifunctional monomers rangefrom 10 to 1000 s, where sorption times τ of 60 to 600 are preferred.

Further, the polymer composition in accordance with the presentinvention may be prepared by compounding the components within suitablemelt mixing devices for preparing polymeric compounds, including inparticular extruders single screw extruders as well as twin screwextruders. Other suitable melt mixing devices include planet extrudersand single screw co-kneaders. Especially preferred are twin screwextruders including high intensity mixing and kneading sections.Suitable melt temperatures for preparing the compositions are in therange from 170 to 300° C., preferably in the range from 200 to 260° C.,and at a throughput of 10 to 500 kg/h and a screw speed of 50 to 200rpm.

As already identified above, the polypropylene composition or the randompropylene copolymer (R-PP) in accordance with the present invention issubjected a visbreaking step. The visbreaking may be carried out in anyknown manner, but typically the present invention envisages chemicalvisbreaking using a peroxide visbreaking agent. Typical visbreakingagents are 2,5-dimethyl-2,5-bis(tert.butyl-peroxy)hexane (DHBP) (forinstance sold under the tradenames Luperox 101 and Trigonox 101),2,5-dimethyl-2,5-bis(tert.butyl-peroxy)hexyne-3 (DYBP) (for instancesold under the tradenames Luperox 130 and Trigonox 145),dicumyl-peroxide (DCUP) (for instance sold under the tradenames LuperoxDC and Perkadox BC), di-tert.butyl-peroxide (DTBP) (for instance soldunder the tradenames Trigonox B and Luperox Di),tert.butyl-cumyl-peroxide (BCUP) (for instance sold under the tradenamesTrigonox T and Luperox 801) and bis(tert.butylperoxy-isopropyl)benzene(DIPP) (for instance sold under the tradenames Perkadox 14S and LupperoxDC). Suitable amounts of peroxide to be employed in accordance with thepresent invention are in principle known to the skilled person and caneasily be calculated on the basis of the amount of polypropylenecomposition and/or random propylene copolymer (R—PP) to be subjected tovisbreaking, the MFR₂ (230° C.) value of the polypropylene compositionand/or random propylene copolymer (R-PP) to be subjected to visbreakingand the desired target MFR₂ (230° C.) of the product to be obtained.Accordingly, typical amounts of peroxide visbreaking agent are from0.005 to 0.5 wt.-%, more preferably from 0.01 to 0.2 wt.-%, based on theamount of propylene polymer employed.

Typically, visbreaking in accordance with the present invention iscarried out in an extruder, so that under the suitable conditions, anincrease of melt flow rate is obtained. During visbreaking, higher molarmass chains of the starting product are broken statistically morefrequently than lower molar mass molecules, resulting in an overalldecrease of the average molecular weight and an increase in melt flowrate.

For the preparation of extrusion molded articles an extrusion blownprocess as known in the art is applied. For instance, for the productionof 1 liter round bottles like used for testing in the inventive work a“Fischer Müller” Blow Molding Machine may be used. The main processingparameters for the production are as follows:

-   -   Temperature profile: 180 to 190° C. applied in extruder, adapter        and head    -   Melt temperature measured: 180 to 190° C.    -   Speed of extruder (revolution per minute; rpm): 11 to 14 rpm    -   Die gap: the die gap was adjusted to get a bottle with a weight        of 40 g with Borealis grade RB307MO    -   Cycle time: 12 to 16 seconds

The present invention will now be described in further detail by theexamples provided below.

EXAMPLES

1. Definitions/Measuring Methods

The following definitions of terms and determination methods apply forthe above general description of the invention as well as to the belowexamples unless otherwise defined.

NMR-Spectroscopy Measurements:

The ¹³C-NMR spectra of polypropylenes were recorded on Bruker 400 MHzspectrometer at 130° C. from samples dissolved in1,2,4-trichlorobenzene/benzene-d6 (90/10 w/w). For the pentad analysisthe assignment is done according to the methods described in literature:(T. Hayashi, Y. Inoue, R. Chüjö, and T. Asakura, Polymer 29 138-43(1988).and Chujo R, et al, Polymer 35 339 (1994).

The NMR-measurement was used for determining the mmmm pentadconcentration in a manner well known in the art.

Randomness

In the FTIR measurements, films of 250-mm thickness were compressionmoulded at 225° C. and investigated on a Perkin-Elmer System 2000 FTIRinstrument. The ethylene peak area (760-700 cm⁻¹) was used as a measureof total ethylene content. The absorption band for the structure -P-E-P-(one ethylene unit between propylene units), occurs at 733 cm^(−1.) Thisband characterizes the random ethylene content. For longer ethylenesequences (more than two units), an absorption band occurs at 720 cm⁻¹.Generally, a shoulder corresponding to longer ethylene runs is observedfor the random copolymers. The calibration for total ethylene contentbased on the area and random ethylene (PEP) content based on peak heightat 733 cm⁻¹ was made by ¹³C⁻NMR. (Thermochimica Acta, 66 (1990) 53-68).Randomness=random ethylene (-P-E-P-) content/the total ethylenecontent×100%.

Number average molecular weight (M_(n)), weight average molecular weight(M_(w)) and molecular weight distribution (MWD) are determined by sizeexclusion chromatography (SEC) using Waters Alliance GPCV 2000instrument with online viscometer. The oven temperature is 140° C.Trichlorobenzene is used as a solvent (ISO 16014).

MFR₂ (230° C.) is measured according to ISO 1133 (230° C., 2.16 kgload).

Ethylene content is measured with Fourier transform infraredspectroscopy (FTIR) calibrated with ¹³C-NMR. When measuring the ethylenecontent in polypropylene, a thin film of the sample (thickness about 250mm) was prepared by hot-pressing. The area of absorption peaks 720 and733 cm⁻¹ was measured with Perkin Elmer FTIR 1600 spectrometer. Themethod was calibrated by ethylene content data measured by ¹³C-NMR.

Content of any one of the C4 to C20 α-olefins is determined with¹³C-NMR; literature: “IR-Spektroskopie für Anwender”; WILEY-VCH, 1997and “Validierung in der Analytik”, WILEY-VCH, 1997.

The xylene cold solubles (XCS, wt.-%): Content of xylene cold solubles(XCS) is determined at 23° C. according ISO 6427.

The gel content is assumed to be identical to the xylene hot insoluble(XHI) fraction, which is determined by extracting 1 g of finely cutpolymer sample with 350 ml xylene in a Soxhlet extractor for 48 hours atthe boiling temperature. The remaining solid amount is dried at 90° C.and weighed for determining the insolubles amount.

Strain Hardening Behaviour (Melt Strength):

The strain hardening behaviour is determined by the method as describedin the article “Rheotens-Mastercurves and Drawability of Polymer Melts”,M. H. Wagner, Polymer Engineering and Science, MID-APRIL 1SW, Vol. 36,NO. 7, pages 925 to 935. The content of the document is included byreference.

For detailed explanation of the measuring method it is also referred tothe FIGS. 1 and 2. FIG. 1 shows a schematic representation of theexperimental procedure which is used to determine strain hardening.

The strain hardening behaviour of polymers is analysed by Rheotensapparatus (1) (product of Göttfert, Siemensstr. 2, 74711 Buchen,Germany) in which a melt strand (2) is elongated by drawing down with adefined acceleration. The haul-off force F in dependence of draw-downvelocity v is recorded.

The test procedure is performed in a standard climatized room withcontrolled room temperature of 23° C. and 30 bar. The Rheotens apparatus(1) is combined with an extruder/melt pump (3) for continuous feeding ofthe melt strand (2). The extrusion temperature is 200° C.; a capillarydie with a diameter of 2 mm and a length of 6 mm is used. The strengthlength between the capillary die and the Rheotens wheels is 80 mm. Atthe beginning of the experiment, the take-up speed of the Rheotenswheels was adjusted to the velocity of the extruded polymer strand(tensile force zero): Then the experiment was started by slowlyincreasing the take-up speed of the Rheotens wheels until the polymerfilament breaks. The acceleration of the wheels was small enough so thatthe tensile force was measured under quasi-steady conditions. Theacceleration of the melt strand (2) drawn down is 120 mm/sec².

The Rheotens was operated in combination with the PC program EXTENS.This is a real-time data-acquisition program, which displays and storesthe measured data of tensile force and drawdown speed.

The schematic diagram in FIG. 1 shows in an exemplary fashion themeasured increase in haul-off force F (i.e. “melt strength”) versus theincrease in draw-down velocity v (i.e. “drawability”).

Haze Measurement on Bottles

Instrument: Haze-gard plus from BYK-Gardner

Testing: according to ASTM D1003 (as for injection molded plates)

The Bottles:

It is measured on the wall of the bottles. The top and bottom of thebottles is cut off. This round wall is then split in two, horizontally.Then the haze measurement and the wall thickness are done in six placesaround this wall, close to the middle. Then the haze value is reportedas average of this six parallels.

Gloss Measurement on Bottles

Instrument: Sceen TRI-MICROGLOSS 20-60-80 from BYK-Gardner

Testing: ASTM D 2457 (as for injection molded plates)

The Bottles:

It is measured on the wall of the bottles. The top and bottom of thebottles is cut off. This round wall is then split in two, horizontally.Then this wall is cut into six equal samples of app. 90×90 mm, just tofit into a special light trap made for testing on injection moldedparts. Then the gloss at 60° is measured on these six samples, and theaverage value is reported as gloss at 60°

Top Load

Aim of this measurement is to determine the stiffness of 1 liter roundbottles. Determined by this method is the deformation force at 1 mm, 2mm and 3 mm deformation of the round bottle. Additionally the maximumforce F_(max) and the deformation in mm at F_(max) are determined.

The bottles have a height of 203 mm. The bottles are produced accordingto the description given below.

Before testing, the bottles are conditioned for 7 days at a temperatureof 23° C. and at relative humidity of 50% (+/−5%). The burr of thebottle orifice is removed.

Top load is tested at universal testing machine of the class 1 accordingto DIN 51221. Bottles to be tested are put between two parallel buffedplates of hardened steel, one plate is fixed and the other plate ismoving. Force is recorded and results are given as F. (N) andDeformation at Maximum Force (mm).

Eight bottles are tested with speed of 10 mm/min by using 2.5 kN loadcell. The test results of the eight tested bottles give the averagevalue.

Weight Swell

The weight swell is a measurement that shows the fit in process abilityof a polypropylene sample material compared to a defined referencegrade.

The weight swell is defined as the ratio of the weight of a samplebottle, produced at defined reference conditions, to the weight of astandard bottle produced at reference conditions.

The formula is the following:Weight swell(%)=weight of sample bottle (g)/weight of standard bottle(g)×100

Reference conditions are defined as the appropriate set of temperature(° C.), throughput of feeding extruder (rpm) and width of the die gap(mm) needed for the production of standard bottles showing exactly aweight of 40+/−1 g by using a defined standard polypropylene grade usedfor extrusion blow molding. The standard bottles described in thisinvention are produced from Borealis random polypropylene grade RB307MO(ethylene content about 4 wt.-%, MFR₂ (230° C.) about 1.5 g/10 min)under reference condition, meaning condition necessary to get to bottleswith 40 g (+/−1 g).

2. Preparation of the Examples

The components were blended according to Table 1. For stabilization ofthe materials a conventional additive package has been used like 0.2wt/% Irganox B225 (antioxidant masterbatch supplied by Ciba SpecialtyChemicals, Switzerland) and 0.05 wt % Ca-Stearate (CAS-No. 1592-23-0).For the visbreaking step peroxide initiator (Trigonox 101, supplied byAkzo Nobel) was dosed in an amount of 0.015 wt.-%. Blending took placein a twin screw extruder (PRISM TSE24 L/D ratio 40) with two highintensity mixing segments at temperatures between 190 and 240° C. at athrough put of 10 kg/h and a screw speed of 50 rpm. The material wasextruded to two circular dies of 3 mm diameter into a water bath forstrand solidification and then pelletized and dried.

For the production of 1 liter round bottles like used for testing in theinventive work a “Fischer Müller” Blow Molding Machine was used. Themain processing parameters for the production are as follows:

-   -   Temperature profile: 180 to 190° C. applied in extruder, adapter        and head    -   Melt temperature measured: 180 to 190° C.    -   Speed of extruder (revolution per minute; rpm): 11 to 14 rpm    -   Die gap: the die gap was adjusted to get a bottle with a weight        of 40 g with Borealis grade RB07MO    -   Cycle time: 12 to 16 seconds

TABLE 1 Properties of the polypropylene compositions Gloss Gloss TopWeight R-PP HMS α-1 α-2 MFR** Haze inside outside load Swell [g] [g] [g][g] g/10 min % [%] [%] [N] [%] CE 1 99.83 — 0.17 — 1.4 26.0 11 12 240100 CE 2 99.60 — 0.40 — 2.6 17.0 230 75 CE 3 99.60 — — 0.40 1.5 15.0 1413 255 100 CE 4* 99.60 — 0.40 — 3.7 14.0 230 57 IE 1 92.10 7.5 0.40 —2.2 13.9 17 19 280 97 IE 2* 92.10 7.5 0.40 2.6 10.4 19 20 300 101*visbroken **“MFR” is MFR₂ (230° C.) R-PP: is the commercial randompropylene ethylene copolymer “RB307MO” of Borealis with an ethylenecontent of 3.9 wt.-%, a MFR₂ (230° C.) of 1.5 g/10 min, a density of 902kg/m³, a branching index g′ of 1.0 and a xylene cold soluble fraction(XCS) of 7.0 wt.-%. HMS: is the commercial high melt strengthpolypropylene Daploy ™ WB180HMS of Borealis based on a propylenehomopolymer, wherein the high melt strength polypropylene Daploy ™WB180HMS has a density of 905 kg/m³, a melting point of 165° C., MFR₂(230° C.) of 6.0 g/10 min, a melt strength of 11.5 cN at a maximum speedof 242 mm/s, a xylene cold soluble fraction (XCS) of 2.5 wt.-% and abranching index g′ of 0.64. α-1: is the commercial α-nucleating agentMillad 3988 (bis (3,4,-di-methyl-benzylidene) sorbitol) α-2: is thecommercial α-nucleating agent Millad NX 8000(Nonitol,1,2,3,-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol)

We claim:
 1. A method for producing an extrusion blown molded product,comprising the steps of: providing a visbroken polypropylene compositioncomprising a random propylene copolymer (R-PP), a high melt strengthpolypropylene (HMS-PP) and a clarifier, wherein (a) the R-PP comprisesunits derived from propylene and at least another C₂ to C₂₀ α-olefin,and has a xylene cold soluble fraction (XCS) of not more than 15.0 wt-%,(b) optionally the HMS-PP has a branching index g′ of less than 1.0, (c)the C comprises at least one α-nucleating agent clarifier, and (d) thepolypropylene composition has a MFR₂ (230° C.) in the range of 2.0 to6.0 g/10 min. and a visbreaking ratio of (final MFR₂ (230° C.)/initialMFR₂ (230° C.)) of 1.4 to 2.5, wherein further the α-nucleating agent isselected from the group consisting of (i) C₁-C₈-alkyl-substituteddibenzylidenesorbitol derivatives, and (ii) vinylcycloalkane polymer andvinylalkane polymer; and extrusion blow molding said polypropylenecomposition to produce an extrusion blown molded product.
 2. The methodaccording to claim 1, wherein the extrusion blown molded product is abottle.